Camshaft, cam angle detection device, and internal combustion engine

ABSTRACT

A camshaft includes a sensor rotor and a plurality of cams. The sensor rotor includes a base circle, and a projection portion formed on an outer peripheral surface of the base circle. A long diameter part of that one of the plurality of cams which is closest to the sensor rotor is placed within a region sandwiched between a first virtual line extending from the shaft center of the camshaft and a second virtual line extending from the shaft center of the camshaft in an axial view of the camshaft, the first virtual line passes through one circumferential end of the projection portion of the sensor rotor in an axial view of the camshaft, and the second virtual line passes through the other circumferential end of the projection portion of the sensor rotor in an axial view, of the camshaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a camshaft provided in an internal combustion engine, a cam angle detection device for detecting a rotational phase of the camshaft, and an internal combustion engine.

2. Description of Related Art

As a cam angle detection device used for detection of a rotational phase, namely, a cam angle, of a camshaft provided in an internal combustion engine, there has been known a cam angle detection device in which a sensor rotor having a projection portion on its outer peripheral surface is provided in an end of a camshaft, and a cam angle sensor is disposed in the vicinity of the sensor rotor (for example, Japanese Patent Application Publication No. 2012-21844 (JP 2012-21844 A)).

In the cam angle detection device, when a distance between the projection portion and the cam angle sensor changes along with rotation of the sensor rotor, a signal according to a cam angle is output from the cam angle sensor. As the cam angle sensor used for such a cam angle detection device, a digital sensor configured to output different binary detection signals at the time when the projection portion passes in the vicinity of the cam angle sensor and at the time when parts other than the projection portion pass in the vicinity of the cam angle sensor is generally used.

SUMMARY OF THE INVENTION

In recent years, it has been desired that a camshaft is shortened so as to achieve a reduction in space in an internal combustion engine. Even in terms of the camshaft described in JP 2012-21844 A, if the sensor rotor is provided not in the end of the camshaft but between cams, for example, it is possible to shorten the camshaft.

However, in a case where the cam and the sensor rotor are provided closer to each other as such, when a nose of the cam passes in the vicinity of the cam angle sensor, the same detection signal as the detection signal output at the time when the projection portion of the sensor rotor passes in the vicinity of the cam angle sensor may be output from the cam angle sensor.

Accordingly, in such a case, the detection signal corresponding to the projection portion of the sensor rotor and the detection signal corresponding to the nose of the cam are mixed in the detection signal output from the cam angle sensor, thereby resulting in that the cam angle cannot be detected precisely.

The present invention provides a camshaft, an internal combustion engine, and a cam angle detection device each of which is able to achieve a reduction in space in the internal combustion engine and to more precisely detect a cam angle.

A camshaft according to a first aspect of the present invention includes a sensor rotor and a plurality of cams. The sensor rotor includes a base circle, and a projection portion formed on an outer peripheral surface of the base circle so as to be detected by a cam angle sensor. A nose of each of the plurality of the cams includes a long diameter part configured such that its radial length from a shaft center of the camshaft is longer than a radius of the base circle of the sensor rotor. The long diameter part of that one of the plurality of cams which is closest to the sensor rotor is placed within a region sandwiched between a first virtual line extending from the shaft center of the camshaft and a second virtual line extending from the shaft center of the camshaft in an axial view of the camshaft. The first virtual line passes through one circumferential end of the projection portion of the sensor rotor in the axial view of the camshaft. The second virtual line passes through the other circumferential end of the projection portion of the sensor rotor in the axial view of the camshaft.

According to the above aspect, a detection signal corresponding to the nose of the cam is output during a period when a detection signal corresponding to the projection portion of the sensor rotor is output from the cam angle sensor. Accordingly, even in a case where the sensor rotor and the cam are provided close to each other and the nose of the cam is detected by the cam angle sensor, only the detection signal corresponding to the projection portion of the sensor rotor is seemingly output from the cam angle sensor. In view of this, according to the above configuration, even if the sensor rotor is provided closer to the cam, it is possible to restrain an effect of the nose of the cam with respect to the detection signal of the cam angle sensor. As a result, it is possible to achieve a reduction in space for the camshaft and to more precisely detect a cam angle.

In an internal combustion engine including the camshaft of the above aspect, a thrust bearing may be, disposed between the sensor rotor and that journal bearing of the camshaft which is closest to the sensor rotor. According to the above aspect, it is not necessary to separately provide a flange to retain the thrust bearing. As a result, it is possible to achieve a reduction in space in the internal combustion engine and to reduce the number of components.

A cam angle detection device according to a second aspect of the present invention includes a sensor rotor and a cam angle sensor. The sensor rotor is provided on a camshaft including a cam. The sensor rotor includes a projection portion on its outer peripheral surface. The cam angle sensor is configured to output a detection signal of a first prescribed value at the time when the projection portion of the sensor rotor approaches the cam angle sensor and to output the detection signal of a second prescribed value different from the first prescribed value at the time when the projection portion is distanced therefrom. The projection portion is configured such that a first rotational phase range includes a whole second rotational phase range. The first rotational phase range is a rotational phase range of the camshaft in which the projection portion approaches the cam angle sensor and the cam angle sensor outputs the detection signal of the first prescribed value. The second rotational phase range is the rotational phase range of the camshaft in which a nose of the cam approaches the cam angle sensor and the cam angle sensor outputs the detection signal of the first prescribed value.

According to the above aspect, a whole period when the cam angle sensor detects the nose of the cam and outputs a detection signal of the first prescribed value and a period when the cam angle sensor detects the projection portion of the sensor rotor and outputs a detection signal of the first prescribed value overlap with each other. Accordingly, even in a case where the sensor rotor and the cam are provided close to each other and the nose of the cam is detected by the cam angle sensor, only the detection signal corresponding to the projection portion of the sensor rotor is seemingly output from the cam angle sensor. In view of this, according to the above configuration, even if the sensor rotor is provided closer to the cam, it is possible to restrain an effect of the nose of the cam with respect to the detection signal of the cam angle sensor. As a result, it is possible to achieve a reduction in space for the camshaft and to more precisely detect a cam angle.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic drawing illustrating a schematic configuration of an intake camshaft;

FIG. 2 is a sectional view taken along a line II-II in FIG. 1; and

FIG. 3 is a timing chart illustrating a detection signal of a cam angle sensor.

DETAILED DESCRIPTION OF EMBODIMENTS

The following describes one embodiment of an intake camshaft as a cam-angle detection target, and an internal combustion engine including the intake camshaft, with reference to FIGS. 1 to 3. As illustrated in FIG. 1, an intake camshaft 11 is rotatably supported by a plurality of journal bearings 13 provided in cylinder heads 12 of an internal combustion engine 10. A cam pulley 14 is disposed in an end of the intake camshaft 11. The cam pulley 14 is connected to a crankshaft by a timing belt. Hereby, when the crankshaft rotates, the intake camshaft 11 rotates in synchronization with this. Further, the intake camshaft 11 includes a plurality of cams 15 each operating an intake air valve in an opening and closing manner, and a sensor rotor 16 provided adjacent to one of the cams 15 and including a plurality of projection portions 17 formed on an outer peripheral surface thereof.

A cam angle sensor 18 is provided in a position opposed to the outer peripheral surface of the sensor rotor 16. The cam angle sensor 18 is a digital sensor configured such that: when the projection portion 17 of the sensor rotor 16 approaches the cam angle sensor 18, the cam angle sensor 18 outputs a detection signal of a first prescribed value; and when the projection portion 17 is distanced therefrom, the cam angle sensor 18 outputs a detection signal of a second prescribed value different from the first prescribed value. Further, a nose 19 of a cam 15 (151) closest to the sensor rotor 16 is placed in a detectable range of the cam angle sensor 18. Accordingly, when the nose 19 of the cam 15 passes in the vicinity of the cam angle sensor 18, the cam angle sensor 18 outputs a detection signal of the first prescribed value. Note that the sensor rotor 16 and the cam angle sensor 18 function as a cam angle detection device.

Further, as illustrated in FIG. 1, a thrust bearing 20 that rotatably supports the intake camshaft 11 and regulates its axial movement is disposed between the sensor rotor 16 and a journal bearing 13 closest to the sensor rotor 16. Both side surfaces of the thrust bearing 20 in its axial direction abut with the journal bearing 13 and the sensor rotor 16, respectively.

Referring now to FIG. 2, the following describes a positional relationship between the sensor rotor 16 and the cam 151 closest to the sensor rotor 16, more specifically. Note that FIG. 2 is a sectional view taken along a line II-II in FIG. 1, that is, a sectional view of the intake camshaft 11 when viewed from its axial direction.

As illustrated in FIG. 2, a base circle 21 of the cam 151 has the same diameter as a base circle 22 of the sensor rotor 16. The cam 151 is provided with a nose 19 having a diameter larger than that of the base circle 21 of the cam 151. In a radial direction of the intake camshaft 11, a length L1 from a shaft center O of the intake camshaft 11 to an outer peripheral surface of the nose 19 is longer than a radius r of the base circle 22 of the sensor rotor 16. Further, a length L2 from the shaft center O to a tip NP of the nose 19 is the same as a length L3 from a center of the sensor rotor 16 to a tip of the projection portion 17 thereof (L2=L3). The nose 19 is entirely placed within a region R sandwiched between two virtual lines L4, L5 extending from the shaft center O so as to respectively pass through both ends 23 of the projection portion 17, that is, starting points S1, S2 where the projection portion 17 rises from the base circle 22. Note that, in the nose 19 of the cam 151, that part of the nose 19 of which the length L1 from the shaft center O of the intake camshaft 11 to the outer peripheral surface of the nose 19 is longer than the radius r of the base circle 22 of the sensor rotor 16 is referred to as a long diameter part in the following description. Accordingly, in the cam 151 illustrated in FIG. 2, the whole nose 19 corresponds to the long diameter part, and the long diameter part is placed within the region R.

Referring now to FIG. 3, the following describes an operation of the intake camshaft 11 of the present embodiment. Note that, in FIG. 3, a detection signal actually output from the cam angle sensor 18 at the time when the intake camshaft 11 rotates is illustrated by a continuous line, and a virtual detection signal output from the cam angle sensor 18 in response to rotation of the nose 19 at the time when the nose 19 of the cam 151 is assumed a detected part is illustrated by an alternate long and short dash line.

As illustrated by the continuous line in FIG. 3, when the projection portion 17 of the sensor rotor 16 approaches the cam angle sensor 18 due to the rotation of the intake camshaft 11, the cam angle sensor 18 outputs a detection signal of the first prescribed value, and when the projection portion 17 is distanced therefrom, the cam angle sensor 18 outputs a detection signal of the second prescribed value.

Further, as illustrated by the alternate long and short dash line in FIG. 3, when the intake camshaft 11 rotates and the nose 19 of the cam 151 approaches the cam angle sensor 18, the cam angle sensor 18 outputs a detection signal of the first prescribed value, and when the nose 19 of the cam 151 is distanced therefrom, the cam angle sensor 18 outputs a detection signal of the second prescribed value.

In the present embodiment, since the long diameter part, namely, the whole nose 19 of the cam 151 is placed within the region R, the detection signal at the time when the nose 19 of the cam 151 is assumed a detected part is output during a period when the cam angle sensor 18 outputs the detection signal of the first prescribed value in response to the projection portion 17 of the sensor rotor 16, as illustrated by the alternate long and short dash line in FIG. 3. That is, a rotational phase range RC of the intake camshaft 11 in which range the projection portion 17 of the sensor rotor 16 approaches the cam angle sensor 18 and the cam angle sensor 18 outputs the detection signal of the first prescribed value includes a whole rotational phase range Rn of the intake camshaft 11 in which range the nose 19 of the cam 151 approaches the cam angle sensor 18 and the cam angle sensor 18 outputs the detection signal of the first prescribed value. Accordingly, the detection signal at the time when the projection portion 17 of the sensor rotor 16 is detected and the detection signal at the time when the nose 19 of the cam 151 is detected overlap with each other, so that the detection signal output from the cam angle sensor 18 is seemingly the same as the detection signal at the time when only the projection portion 17 of the sensor rotor 16 is assumed a detected part.

Note that, in a case where the cam 151 and the sensor rotor 16 are provided close to each other, if an outside diameter of the sensor rotor 16 is set larger than an outside diameter of the cam 151, it is possible to restrain detection of the nose 19 of the cam 151 by the cam angle sensor 18, and it is possible to precisely detect a cam angle. However, in such a case, since the outer diameter of the sensor rotor 16 is increased, a mounting space of the sensor rotor 16 is increased by just that much. On the other hand, it is not necessary to increase the outside diameter of the sensor rotor 16 in the present embodiment. Accordingly, it is possible to achieve a reduction in space in the internal combustion engine 10 in comparison with a case where the sensor rotor is formed to have a large diameter.

According to the first embodiment described above, it is possible to obtain the following effects. (1) Even in a case where the sensor rotor 16 and the cam 151 are provided close to each other and the nose 19 of the cam 151 is detected by the cam angle sensor 18, only a detection signal to be output at the time when only the projection portion 17 of the sensor rotor 16 is assumed a detected part is seemingly output from the cam angle sensor 18. Accordingly, even if the sensor rotor 16 is disposed in proximity to the cam 151, it is possible to restrain an effect of the nose 19 of the cam 151 with respect to the detection signal of the cam angle sensor 18, thereby making it possible to achieve a reduction in space for the intake camshaft 11 and to more precisely detect the cam angle.

(2) Since the thrust bearing 20 is disposed between the sensor rotor 16 and that journal bearing 13 of the intake camshaft 11 which is closest to the sensor rotor 16, it is not necessary to separately provide a flange to retain the thrust bearing 20. As a result, it is possible to achieve a reduction in space in the internal combustion engine 10 and to reduce the number of components.

Note that the above embodiment can be modified as follows.—In the above embodiment, the length L2 from the shaft center O of the intake camshaft 11 to the tip NP of the nose 19 is generally the same as the length L3 from the shaft center O to the tip of the projection portion 17. However, the lengths L2, L3 thereof may be changed appropriately provided that the whole nose 19, which is the long diameter part, is placed within the region R. Even with such a configuration, it is possible to yield the same effects as the effects (1) and (2).

In the above embodiment, the region R is defined about a projection portion 17 placed on an upper side in FIG. 2 among the projection portions 17 provided in the sensor rotor 16. However, the region R may be defined with respect to the other projection portions 17 in a similar manner, and the long diameter part may be placed in the region R thus defined. Even with such a configuration, it is possible to yield the same effects as the effects (1) and (2).

In the above embodiment, the base circle 21 of the cam 151 has the same diameter as the base circle 22 of the sensor rotor 16. However, the base circle 21 of the cam 151 may have a diameter larger than that of the base circle 22 of the sensor rotor 16, or the base circle 21 of the cam 151 may have a diameter smaller than that of the base circle 22 of the sensor rotor 16. Note that, even in such a case, when the long diameter part in the nose 19 of the cam 151 is placed within the region R, it is possible to yield the same effects as the effects (1) and (2).

In the above embodiment, the thrust bearing 20 is disposed between the journal bearing 13 and the sensor rotor 16, but such a configuration may be omitted. Even in such a case, it is possible to yield the same effect as the effect (1).

A relationship of the rotational phases of the sensor rotor 16 and the cam 151 is determined so that the rotational phase range (the range RC of FIG. 3) of the intake camshaft 11 in which range the projection portion 17 formed on the outer peripheral surface of the sensor rotor 16 is assumed a detected part and the cam angle sensor 18 outputs the detection signal of the first prescribed value includes a whole rotational phase range (the rotational phase range Rn in FIG. 3) of the intake camshaft 11 in which range the nose 19 of the cam 15 is assumed a detected part and the cam angle sensor 18 outputs the detection signal of the first prescribed value. Then, the sensor rotor 16 and the cam 151 may be formed in the intake camshaft 11 in a state where such a relationship is satisfied. Even with such a configuration, it is possible to yield the same effect as the effect (1).

The above embodiment exemplifies an example in which the intake camshaft 11 is assumed a cam-angle detection target. However, even in a case where an exhaust camshaft is assumed a cam-angle detection target, if the same configuration is employed, it is possible to obtain the above effects. 

1. A camshaft comprising: a sensor rotor including a base circle, and a projection portion formed on an outer peripheral surface of the base circle so as to be detected by a cam angle sensor; and a plurality of cams each having a nose including a long diameter part configured such that its radial length from a shaft center of the camshaft is longer than a radius of the base circle of the sensor rotor, wherein the long diameter part of that one of the plurality of cams which is closest to the sensor rotor is placed within a region sandwiched between a first virtual line extending from the shaft center of the camshaft and a second virtual line extending from the shaft center of the camshaft in an axial view of the camshaft, the first virtual line passes through one circumferential end of the projection portion of the sensor rotor in the axial view of the camshaft, and the second virtual line passes through the other circumferential end of the projection portion of the sensor rotor in the axial view of the camshaft.
 2. An internal combustion engine comprising: the camshaft according to claim 1; a plurality of journal bearings that rotatably support the camshaft; and a thrust bearing placed between the sensor rotor and that one of the journal bearings which is closest to the sensor rotor.
 3. A cam angle detection device comprising: a sensor rotor provided on a camshaft including a cam, the sensor rotor including a projection portion on outer peripheral surface of the sensor rotor; and a cam angle sensor configured to output a detection signal of a first prescribed value when the projection portion of the sensor rotor approaches the cam angle sensor and to output the detection signal of a second prescribed value different from the first prescribed value when the projection portion is distanced from the cam angle sensor, wherein: the projection portion is configured such that a first rotational phase range includes a whole second rotational phase range; the first rotational phase range is a rotational phase range of the camshaft in which the projection portion approaches the cam angle sensor and the cam angle sensor outputs the detection signal of the first prescribed value; and the second rotational phase range is the rotational phase range of the camshaft in which a nose of the cam approaches the cam angle sensor so that the cam angle sensor outputs the detection signal of the first prescribed value. 